**6. Liming in sugarcane regrowth areas**

**5. Gypsum**

Agricultural gypsum, 10CaSO4

176 Sugarcane - Technology and Research

CaC2+ contents are lower than 0.4 cmolc

**Layer (cm) Exchangeable calcium (cmolc**

Source: adapted from [15].

is not very high, the response to gypsum may be lower.

.2H<sup>2</sup>

the reaction between sulfuric acid and phosphate rocks used to produce phosphoric acid. Gypsum applied to soil does not neutralize soil acidity but decreases aluminum saturation and increases base saturation of the subsurface, providing conditions for a further development and deepening of the sugarcane root system. It is recommended to apply gypsum when

at the 20–40 cm layer. The application of gypsum will lead to the improvement of the root environment at layers below arable ones, an effect that lasts for several years. For this reason, the annual reapplication of gypsum is not necessary. In areas with sugarcane straw or organic residues on the soil, and if the contents of Ca2+ are not very low and/or aluminum saturation

The doses of gypsum to be applied may be based on the need for liming, or on soil texture. The amount of gypsum to be applied varied between 25 and 30% for the need for liming, multiplied by a depth correction factor (profile to be corrected/20). For example, the amount of limestone to be applied was 3.0 t ha−1, and improvement of the root environment at the 20–60 cm layer is desired. Then, the amount of gypsum will be equal to 1.5 t ha−1[(3.0 x 0.25) x (60–20)/20]. When the doses of gypsum to be applied are based on soil texture, the following

Gypsum is applied in total area and may or may not be incorporated into the soil. When it is not possible to use it, mainly because of difficulty in acquiring it in small quantities, a fact that usually happens with micro and small farmers, one should choose to apply simple superphosphate as a source of phosphorus because this fertilizer contains calcium sulfate. In a study conducted by [15], limestone and gypsum rates were studied in a sugarcane crop cultivated in medium texture soils with a low cation exchange capacity. A relation between calcium levels in the soil and growth of the root system was also observed. Twenty-seven months after the beginning of the study, in a treatment with the application of 2.8 t of gypsum per hectare, the highest yield of biomass and industrializable shoots occurred. By soil

recommendation can be used [8]: dose to be applied (kg ha−1) = clay (g kg−1) x 6.0.

0–25 2.10 4.4 29.93 26–50 1.37 3.0 20.41 51–75 0.90 2.4 16.33 76–100 0.82 2.0 13.61 101–125 0.70 1.8 12.24 126–150 0.60 1.1 7.48

**Table 2.** Calcium content in the soil and growth of sugarcane root system in a soil that received limestone and gypsum.

O, a by-product of the fertilizer industry, originates from

dm−3 and/or aluminum saturation is greater than 20%

 **dm−3) Root mass (g dm−3) % of root system**

Soil calcium and magnesium contents decrease during sugarcane cycles both by the removal of bases by harvests and by acidification caused by nitrogenous fertilizers. This effect is demonstrated in the long-term study (**Figure 4**) conducted by [15, 16]. These authors evaluated the reacidification of a soil cultivated with sugarcane by five cuts.

Initially, the soil presented, at the layers 0–20 and 20–50 cm, a base saturation of 15 and 7%, respectively. At the time of preparation of the soil for planting sugarcane, 2.5 t of limestone and 1.5 t of gypsum were applied per hectare. Soil chemical changes in plant cane and regrowth are shown in **Figure 4**. After plant cane thinning, base saturation at the layers 0–20 and 20–50 cm was, respectively, 52 and 38%; by the fifth cut, the values were similar to those observed at the time of reforestation.

The authors of this chapter have recommended liming for regrowth areas when there is a base saturation of less than 50% at the 0–20 cm layer. The application of corrective should be in the total area preceding crop treatments and calculating the necessary amount as previously described.

**Figure 4.** Changes in the base saturation of a soil cultivated with sugarcane. Source: adapted from [15, 16].
